The present invention generally relates to a cooling device for a mounting module, and more particularly, to a cooling device which is capable of lowering a temperature of a small flat heat generating device such as an integrated circuit chip.
Recently, circuits used for electrical devices such as a personal computer, information processor, work station and server are highly integrated and the capacity of semiconductor devices mounted on a control plate circuit has greatly increased. This results in a temperature raise in such electrical devices and therefore there is a need to dissipate the heat generated from circuit plates or the semiconductor devices in an efficient manner.
FIGS. 1A and 1B are diagrams for explaining a conventional cooling device for a mounting module.
A cooling device 11A shown in FIG. 1A is comprised of a printed board 12, circuit elements 13, a heat sink 14 and conductive members 15. A predetermined number of circuit elements 13 such as semiconductor chips are mounted on the printed board 12 and the heat sink 14 having the shape of a flat plate is located above the circuit element 13. The back of the heat sink 14 is connected to the upper surface of each of the circuit element 13 via the conductive member 15 which is usually made of a silicon compound. Thus, the heat generated from the circuit elements 13 is dissipated from the heat sink 14.
The above-mentioned conductive member 15 makes it possible to effectively transmit the heat generated from the circuit elements 13 by supplementing the surface flatness, surface roughness and surface inclination so as to decrease a thermal resistance at a contacting surface (i.e., increase in the contacting surface area). However, it is effected by the thickness of the conductive member 15, which has a certain thermal resistance, upon heat dissipation. The thermal resistance R of the conductive member 15 may be expressed by the following formula (1): EQU R=t/(.lambda..multidot.A) (1)
wherein .lambda. indicates the thermal conductivity W/(m K)! of a conductive member, A indicates a conductive area m.sup.2 ! of the conductive member, and t indicates a mean thickness m! of the conductive member.
FIG. 1B is a diagram showing another conventional cooling device 11B comprising a printed board 12, circuit elements 13, a conductive member 15, a cooling header 21, a block 22, a spring 23 and a heat sink (not shown in the figure). The cooling header 21 is located above the circuit elements 13 mounted on the printed board 12. The cooling header 21 has a hole 21a in a position corresponding to the position of each of the circuit elements 13 and the block 22 is inserted in the hole 21a so that it is in contact with the circuit element 13 via the conductive member 15. The spring 23 presses the block 22 towards the circuit element 13 to assure the contact between the block 22 and the circuit element 13. Heat is transmitted from the block 22 to the cooling header 21 by physical contact between the two or by use of a gas.
In the above-mentioned cooling device shown in FIG. 1B, since the block 22 is pressed to the circuit element 13 by the spring 23, the thickness t.sub.1 of the conductive member 15 is made thinner and the thermal resistance R becomes smaller compared with the case shown in FIG. 1A, and hence the thermal conductivity and the dissipating efficiency may be improved.
However, the cooling device 11B shown in FIG. 1B has some disadvantages. For instance, since the block 22 is pressed to the circuit element 13 by the elastic force of the spring 23, although it is capable of equalizing the difference in the thickness of the conductive member 15, a load applied to the circuit element 13 is increased by, say, vibration and there is a danger that solder balls 16 connecting the circuit element 13 to the printed board 12 may be broken or the circuit element 13 itself destroyed. Also, if the elastic force of the spring 23 is attenuated in order to avoid the above problems, the block 22 may be easily shaken by an outer force and the thickness t.sub.1 of the conductive member 15 may be changed. Thus, there are possibilities that the heat dissipating efficiency of the device is decreased and the cooling performance is lowered.